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Biosynthesis of Abscisic Acid (ABA): Plants and Fungi use different pathways

Viaud's publication in Environmental Microbiology
BIOGER scientist Muriel Viaud and collab. published an article in which they investigated the genome of an ABA-overproducing strain of the gray mold agent Botrytis cinerea and identified a sesquiterpene cyclase as the key enzyme responsible for the biosynthesis of ABA in fungi.

Strikingly, some phytopathogenic fungi are able to produce the well-known plant hormone abscissic acid (ABA). While biosynthesis of ABA in plants is derived from carotenoid, chemistry studies demonstrated that fungal ABA is produced by the direct cyclisation of farnesyl diphosphate (FPP) followed by oxidation steps. Previous studies in Botrytis cinerea identified a cluster of co-localized genes (Bcaba1 to Bcaba4) encoding P450 mono-oxygenases that are responsible for the final oxidation steps, but the key enzyme required for the cyclisation of FPP in fungi remained unknown so far.  

In collaboration with the groups of I. G. Collado and C. Garrido (University of Cadiz, Spain), we identified the gene Bcaba5 encoding the sesquiterpene cyclase (STC) acting as the key enzyme for ABA production in B. cinerea. While fungal genes contributing to the biosynthesis of one secondary metabolite are usually clustered at one genomic locus, Bcaba5 is physically independent from the locus that contains Bcaba1 to Bcaba4. Inactivation of the Bcaba5 gene confirmed that the fungal ABA biosynthesis route is distinct from the plant one and paved the ways for further studies (i) to decipher the fungal ABA biosynthetic pathway and to improve the industrial production of this hormone, (ii) to investigate the evolution of un-clustered secondary metabolism genes in fungi, and finally (iii) to elucidate the enigmatic role of ABA in fungal/plant interactions.


Izquierdo-Bueno I, González-Rodríguez VE, Simon A, Dalmais B, Pradier JM, Le Pêcheur P, Mercier A, Walker AS, Garrido C, Collado IG, Viaud M. Biosynthesis of abscisic acid in fungi: Identification of a sesquiterpene cyclase as the key enzyme in Botrytis cinerea. Environmental Microbiology. 2018 Apr 30. doi: 10.1111/1462-2920.14258.